Explosive projectiles must be capable of being handled safely under considerable stress and environmental conditions. In addition, explosive projectiles must be capable of detonating at the proper time. Depending on the application, this proper time may be before impact, at a specific point during flight, during impact, or at some time delay after impact. As used herein, the terms “warhead,” “explosive device,” and “explosive projectile” are generally used to refer to a variety of projectile type explosives, such as, for example, artillery shells, rockets, bombs, and other weapon warheads. To determine the proper detonation time, these explosive projectiles frequently employ fuzes.
A fuze subsystem activates the explosive projectile for detonation in the vicinity of the target. In addition, the fuze maintains the explosive projectile in a safe condition during logistical and operational phases prior to launch and during the first phase of the launch until the explosive projectile has reached a safe distance from the point of launch. In summary, major functions that a fuze performs are; keeping the weapon safe, arming the weapon when it is a safe distance from the point of launch, and initiating detonation of the warhead at some definable point after launch.
The first two functions of keeping the weapon safe and arming the weapon are conventionally referred to as safing and arming. Safety and Arming (S&A) devices isolate a detonator from the warhead booster charge until the explosive projectile has been launched and a safe distance from the launch vehicle is achieved. At that point, the S&A device removes a physical barrier from the explosive train, which effectively arms the detonator so it can initiate detonation at the appropriate time.
For maximum safety and reliability of a fuze, the sensed forces or events must be unique to the explosive projectile when deployed and launched, not present during ground handling or pre-launch operations. Most fuzes must determine two independent physical parameters before determining that a launch has occurred and a safe separation distance has been reached. The first environment utilized in many S&A devices is setback acceleration. Setback acceleration when the projectile is launched is a relatively easy environment to sense. The second environment can be based on a number of different parameters such as elapsed time, barrel escape, and turns counting.
In safety and arming devices using elapsed time and turns counting, the second environment is sensed and determined with electronic elements. However, for simplicity and safety, it may be desirable to have two different physical environments determined with mechanical systems.
Further, prior devices may be difficult to modify for use in projectiles of various sizes, especially smaller projectiles. It may be desirable to design a safety and arming device which is able to be used in several different size rounds. In addition, it may also be desirable to include the reliability and accuracy of electronics for some timing and control functions in addition to the safety afforded by mechanical obstruction of a firing train. By doing so, improvements in performance, reliability, and producibility may be provided.
There is a need to improve the overall safety and reliability of safety and arming devices in comparison to existing devices by combining electro-mechanical systems including at least two environments sensed by new and different mechanical systems.